A modified clear twin block appliance for treatment of class II malocclusion: a randomized clinical trial.

Abstract

Background: Skeletal Class II malocclusion is commonly treated with functional appliances, but bulkiness and discomfort usually affect the compliance. Modifications of these appliances using clear thermoplastic materials could improve comfort and esthetics; though clinical evidence remains limited.

Objective: To assess the clinical effectiveness of a Modified Twin Block (MTB) appliance, fabricated from 2 mm biocompatible polyethylene terephthalate modified with Glycol (PETG) thermoplastic material, in comparison with the Conventional Twin Block (CTB), for treatment of skeletal Class II due to mandibular retrognathism.

Subjects and methods: This multicenter, single-blinded randomized clinical trial included 50 adolescents, at the peak of pubertal growth (CS -3). Patients were randomly assigned to two parallel groups treated with either a CTB or MTB appliance, both incorporating a midline screw for maxillary expansion. Appliances were worn full-time and the expander was activated twice weekly. The records including cephalograms were taken pre- and post-treatment to evaluate skeletal (sagittal and vertical) and soft tissue changes. Dental arch expansion was assessed using standardized 3D digital model superimposition on palatal landmarks, and overjet/overbite changes were clinically recorded. Patient perception was evaluated using a validated questionnaire. Data were analyzed using paired and independent t-tests.

Results: All patients completed the trial without dropout. Baseline characteristics were comparable between groups, with no significant differences in 20 out of 24 variables. Both the CTB and MTB groups showed significant improvements in skeletal, soft tissue, and dental parameters post-treatment (P < 0.05). Between-group comparison revealed a statistically significant improvement in ANB angle favoring the MTB group (P = 0.004), while vertical skeletal and soft tissue changes showed no significant differences (P > 0.05). The MTB group also demonstrated a significantly greater overbite reduction (P = 0.005) and higher dental arch expansion (P = 0.001), particularly in the molar region. No significant difference was found in active treatment duration. Patient perception data showed significantly more favorable experiences with the MTB appliance in 13 out of 36 questionnaire items, particularly regarding comfort, hygiene, function, and psychosocial impact.

Limitations: Double blinding was not feasible due to clear visual differences between the appliances.

Conclusions: The MTB appliance is effective in treating growing patients with skeletal Class II due to mandibular retrognathism and is comparable with slight advantageous results to CTB appliance.

Trial registration: NCT06116500.